1. Field of the Invention
The present invention relates to the field of percutaneous transluminal treatment of blood vessels, aneurysms, and, particularly refers to a modular graft device for treatment of an aorta aneurysm by replacement or encasement of the affected aorta wall with the inventive graft device.
2. Description of the Prior Art
As it is well known in the art, an aneurysm is a widening or dilation of a blood vessel, artery or vein, caused by thinning of the vessel wall. The rupture of the vessel wall is a lethal complication as long as it results in massive hemorrhage. Aneurysms usually occur in arteries but may also be seen in the heart after local damage, or in veins.
Arterial aneurysms are more common than venous and they may be caused by congenital thinning of the muscular portions of the artery, during atherosclerotic degeneration of the aorta or of the carotid or basilar arteries, by trauma to a vessel wall, by infectious injury, or by degeneration from other causes. The likelihood of rupture is increased by high blood pressure.
An aneurysm in the largest artery in the human body, the aorta, will therefore result in a very important situation. The aorta is the primary vessel carrying blood from the heart to the rest of the circulatory system. The aorta arises from the base of the left ventricle of the heart and arches over and backward to the left front side of the vertebral column, or spine. Then, it passes downward along the spine and divides into the common iliac arteries, which supply blood to the extremities.
For descriptive purposes, the aorta is usually divided into the ascending aorta, the aortic arch, the thoracic descending aorta, and the abdominal aorta. The renal arteries, mesenteric arteries, and many other branches arise from the abdominal aorta.
The walls of the aorta are quite thick and consist primarily of strong, elastic connective tissue. The distensibility of the aorta and its major branches is such that this central reservoir acts as a second heart pump.
A widely used technique for treating a patient harboring an aneurysm is the percutaneous transluminal angioplasty, generally used in the treatment of coronary heart diseases, which technique involves the widening of the arteries that have been dangerously narrowed under the effects of the atherosclorosis, that is, by the buildup of deposits called plaque on their interior walls. A flexible tube, or catheter, is first inserted through a skin incision into an artery. The catheter is manipulated transluminally until it reaches the constriction site. A small balloon at the end of the catheter is then inflated, compressing the plaque and widening the passage. Although this procedure has been largely used since the 1970s, the PTA has been generally restricted to some vessels, coronary arteries, for example, but the use of balloons has not been entirely successful in larger vessels like the aorta because of, among other things, the strong calcification of the plaques.
In addition to the foregoing, with a ruptured aneurysm, a person may be treated with reduction of blood pressure and replacement of the weakened vessel by a graft or encasement in plastic, or mechanically stopping blood flow to or through the aneurysm.
The use of graft devices has been found successful in the treatment of abdominal aortic aneurysms where a graft device comprising an upper main portion and two pending limbs is inserted into the aorta with the main portion retained in the proximal end of the aorta and respective distal ends of the limbs are inserted and retained into the respective iliac arteries, thus replacing the aortic walls by the graft. However, the aortic aneurysms are very often heavily calcified and strongly narrowed by the atherosclerotic plaques. Under these circumstances, and perhaps due to a side effect, the diameter of the iliac arteries tend to dilate with the result that, frequently, the diameter of the aorta, in the zone harboring the aneurysm, that is the distal aorta, is smaller than the sum of the diameters of both iliac arteries. In practice, for example, if the distal aortic diameter is 20 mm and the iliac artery diameter exceeds 11 mm, a 12 mm iliac graft device is necessary to have the distal ends of the graft limbs inserted and retained into the respective iliac arteries. Thus, each graft limb must have a diameter of 12 mm, the graft limbs being extending into and along the distal aortic aneurysm of 20 mm, which, in addition, as stated above, is heavily calcified and rigid. Therefore, the graft limbs with 24 mm (12 mm+12 mm) will be constrained under the restricted section of the aneurysm. More particularly, the exceeding 4 mm in the diameter will be compressed by the aneurysm. While the graft construction and the materials used in its manufacture make the graft device to be flexible enough to be located into the distal aorta, through the restricted section thereof, angulation and compression of the graft limbs could be responsible for the occurrence of limb occlusion and the resulting ischemia of the limbs.
In view of the foregoing it would be desirable to have a graft device capable of being easily inserted and located into a distal aorta with aneurysm, but capable also of being accommodated in the restricted section without being impaired by the smaller diameter available at the restricted section of the aorta.